Born on May 23, 1901 he professed his vows on July 1, 1927. He was ordained on June 15, 1933. Preaching was essential to the life and breath of Father Flynn. From 1934 to 1942 he preached parish missions. Earlier he had graduated from New York University with a business degree. So he was assigned to the West Springfield, Massachusetts retreat house in 1942. Each year 1,100 men made retreats. Six years later 3,800 made a yearly retreat. In 1948 he took that love of the retreat movement to begin Holy Family Retreat House, West Hartford, Connecticut. He along with laymen Jerry Crowley bulldozed the land. In February 1951 the retreat house opened. Key was his ability to have the laymen promote the retreat house to each other. He launched the Altare Dei Society for living and deceased benefactors and friends of the Passionists. His Family Rosary Crusade was popular. Later he was transferred to Brighton, Massachusetts where he organized the National Retreat Convention which was the precursor to Retreats International with offices at Notre Dame University. At seventy years of age he was back in West Hartford to inaugurate the Moral Leadership Program with ethical standards and Gospel values. Later he showed interest in vocations, especially the conservative and devotional minded Legionnaires of Christ.
There is no doubt that the Passionist Retreat Movement was a success because of his efforts to promote this ministry.
His brother Cronin was also a Passionist priest and his sister Marie Cronin was a member of the Maryknoll community.